Bass
TRN TA4 better bass control than TRN TA3.
TRN TA3 has bloomy in some tracks.
TRN TA4 has tighter, deeper and slightly better rumble than TRN TA3.
Good impact and intensity , makes it feel more realistic.
TRN TA4 is clearer, cleaner, tighter and a little quicker. There's no bloominess like TRN TA3.
Mids
TRN TA4 has instruments and vocals little clearer than TRN TA3.
Lively, breezy and emotional.
TRN TA4 has slightly drier vocals than TRN TA3.
But TRN TA4 has smoother vocals than TRN TA3 because TRN TA3 has a nasal sound.
TRN TA3 is slightly juicier and has slightly thicker texture. That makes vocals a bit clearer in level of contrast.
Both have intimate vocals and lush.
Treble
TRN TA4 reduces aggression and harshness in TRN TA3.
TRN TA4 has more airiness than TRN TA3 that makes it feel more smoother and better control.
It feels like the brightness has decreased slightly but it doesn't reduce the sparkle.
Technical & Soundstage & Imaging
TRN TA4 is wider than TRN TA3 and more airiness than TRN TA3.
TRN TA4 has separation instruments better than TRN TA3 and better imaging.
TRN TA4 is easier to listen to and more comfortable to listen to.
Both have average resolution and detail retrieval from budget IEMs.
Overall, TRN TA4 has slightly better technique than TRN TA3, maybe around 10%.
Some people think TRN TA3 is warmer, it will be more musical. I think it's not the only deciding factor.
If you're satisfied with TRN TA3's vocals and don't mind bloomy bass and sibilance on some tracks, stay with TRN TA3.
But if you don't have TRN TA3 yet, go for TRN TA4 for better techniques and clarity.
TRN TA4 and TRN TA3 has natural vocals and timbre comes from DD which is a perceptible charm and
separates it from DD Bass.
What I would like to say to IEMs brand is I think the first thing to consider is the timbre and vocals, not tonal balance.
What's often found is timbre and vocals that come with metallic and plasticky from BAs Drivers.
Or even when using DD Driver, it comes out unnatural.